Tire Pressure....

[thelarkbox]

What tire pressure would you advise for a sit up n beg city bike with 700x40 tires. supporting upto 130-135kg on roads in not the best condition.
Solid frame and forks, No suspension.

Bike + rear hub motor battery 22kg (15kg bike, 7 kg ebike kit)
me 90kg+
Max luggage 20 kg (5-10kg daily)

Me powered top speed from 36t:11t is just about 15mph @ a lento cadence circa 50bpm. according to the new speedo ( cadence could be slower im relying on muscle memory to inform me sat here typing.)

I think i may have over inflated tyres but road race tables indicate even higher pressures than i run at?? Cant find tables focused on the casual bike rider..

Ive already bled 10 psi from my tyres but still bounce..

At even lower pressures i fear 'snake bites from the wheel bottoming out over the frequent road faults, this has happened frequently when i have not checked tires before going out.

But im getting a lot of rear wheel bounce from the speed provided by the new hub motor and im sat full weight on the cycle saddle.

When ridding at this speed without added power i am generally animated in the saddle or fully out of it unless rolling downhill, and then i would balance on the pedals at the first sign of a rough ride. .

Ive only noticed the extra bounce in my back wheel since fitting the Ebike kit. But its on local quiet not hilly residential roads that I regularly pedal at full pelt?? the only difference being while under e power im sat in the saddle fully..

Am I chilling too much just sitting on the saddle of my ebike just adding to the power from the motor? Should i be ridding an ebike like a horse or a trial bike, carrying my weight in my legs constantly ready to lift as the road demands?

First time i experienced the 'bounce' I almost lost control, I did loose everything carried in the bike boxes including a crate of pop. Thankfully it was a very quiet rd and i could park up and retrieve the shopping and only the loo roll and not the cola hit a parked car. .

 

[Raboa]

The max pressure of my tyres is 65psi, I run them at 55psi, 10psi below max.

 

[Az.]

You can add suspension stem and seat post for increased comfort.
Personally I ride bike like a horse. Secure cargo, reduce speed and avoid potholes.

 

[Nealh]

I ride with max 50psi with 700c x 42c tyres and often at 45 psi, the lower psi offers better ride comfort vs higher psi imo. For me I anticipate the terrain and will shift my weight for potholes or lumps /bumps, this mitigates punctures from snakebites .

 

[cyclebuddy]

I've only noticed the extra bounce in my back wheel since fitting the Ebike kit...

Carrying 130kg (suggested max payload is often 120kg), on a new rear hub motor wheel you maybe need to check/tighten your spokes from time to time, especially while that wheel is still bedding in.

 

[guerney]

I ride with max 50psi with 700c x 42c tyres and often at 45 psi, the lower psi offers better ride comfort vs higher psi imo.

I agree. At 50psi I was bouncing about all over the place last night, it was a slower but comfier ride at 40 to 45psi.

 

[Cadence]

700c x 38 - 50psi front. 60 rear. Rear motor and battery on rack.
26" X 1.95" - 40 front. 45 rear. Rear motor and downtube battery.
The wider 26" tyres are much more comfortable than the 700c.
I keep clear of potholes and ruts wherever possible, but when unavoidable (and over speed bumps) I put most of my weight on the pedals, loosen grip on the handlebars and let the bike "pivot" around the bottom bracket.

 

[guerney]

Bit hard to avoid these last night (there was a SUV behind me), bouncing over which loosened one of my lights... ...and perhaps a filling...

 

[Jodel]

I'm inclined to agree with Andy Blance at Thorn cycles that many riders use tyre pressures that are far too high. Have a look at his suggestions on Page 40 of the Thorn Mega-Brochure: http://www.sjscycles.com/thornpdf/thorn_mega_brochure.pdf

Frank Berto's method of aiming for a 15% deflection when loaded works well for me. With a tandem & riders weighing 160KG, I use 700 x 38 Schwalbe Marathon Plus tyres inflated to 55-60psi front / 60-65psi rear. Conventional wisdom would suggest that those pressures are too low, but they have been fine for me with the strong / inflexible sidewalls of the Schwalbe tyres.

Tire Pressure Take-Home

What is the 'correct' tire pressure for your bike? The simple answer is: Whatever feels right to you. Confused? Here is how it works: In the past, many riders inflated their tires to the maximum pressure rating. Now most cyclists now recognize that the optimum pressure often is much…

www.renehersecycles.com

 

[Nealh]

My front tends to be up to 10 psi lower then the rear.

 

[thelarkbox]

Thanks all, My perhaps foolish understanding was the optimum pressure was one that resulted in just the central inch or so of the tire flattened on the road and when viewed from above the tire should not appear to bulge more than 1/16-3/8" either side..

so i was running with 50 psi on the front and 65 at the rear before the hub motor.

I was hesitant to state my pressures in the OP as i blew a tube when fitting the hub wheel 1st time and when i casually mentioned to the chap in the h/w shop that a tube blew on me at close to 60 psi, i detected the raising of an eyebrow and glance between colleagues. Which got me thinking and i tried lower pressures of about 50 psi in the rear before even ridding the ebike at all.. and still i get bounce!!.

@guerney Yikes.. I hope the filling reference was a joke to illustrate the jolt you must have endured.

@Jodel DEFLECTION is the magic word, as soon as i googled tire deflection, as tbh i didnt really understand it in context, i get all the tire pressure charts (non pro) i was looking for before - and im not too far off with my age old understanding..

@cyclebuddy - I would Never have thought about spoke tension unless a wobble had appeared in the rim.. Thanks i guess i should add spoke spanner to the shopping list ..

@Cadence, Me too as a rule, but perhaps with being a bit distracted by new ebike controls and approaching such hazards quicker thanks to the hub motor I have not been reacting quickly enough, I have yet to ride the ebike anywhere i haven't pedaled many times before.. (slower)

@Az the problem with aftermarket suspension add ons is good stuff aint cheap and my ebike is based on a £250 when new 4 yrs ago bike. Oh and i am Very Cheap, I have checked out ebay for used suspension options, even forks and whole frames, but i fear that in itself is a whole new rabbit hole i am not quite ready for.

@Nealh I think you and others have hit the nail on the head and i need to ride much more actively.
Who would have thought it? an ebike needs a whole new set of ridding skills DOH!

I think my expectations had been skewed from seeing all the big fat import ebikes with their recumbent riders that appear every now and again on the cycle track, and it was kinda fun if not a little problematic trying to emulate them.. Bt my attempt to remain street legal on an old boneshaker conversion Needs an active rider ..

I shall also drop my rear pressure a bit too and keep my fingers crossed. against punctures.. lets try 45psi
at the rear and 40 at the front

Thanks again for All the input, Its been very useful, and informative.

TLDR I am the problem !

 

[Scorpio]

My riding is similar to yours (same weight bike + rider + luggage, badly surfaced roads)

My village highstreet is a mess - half my lane is badly surfaced as in your photo - I always ride near the white line regardless of any traffic behind me. It's just a few hundred yards, my speed isn't too slow, and it's a lot safer than riding over the potholes near the kerb.

Fitting front suspension forks might also help you, I got a cheap pair a couple of years ago from Bankrupt Bike Parts and they make riding a lot nicer.

forks | eBay

 

[thelarkbox]

My riding is similar to yours (same weight bike + rider + luggage, badly surfaced roads)

My village highstreet is a mess - half my lane is badly surfaced as in your photo - I always ride near the white line regardless of any traffic behind me. It's just a few hundred yards, my speed isn't too slow, and it's a lot safer than riding over the potholes near the kerb.

Fitting front suspension forks might also help you, I got a cheap pair a couple of years ago from Bankrupt Bike Parts and they make riding a lot nicer.

forks | eBay

similar bike styles perhaps? but not my rd photo thankfully, im dealing with donkeys years of tarmac rough top ups and patches many inches tall, others just shallow depressions as well as the pot holes... but quiet residential streets little or no traffic hence my feeling free to try top ebike speed



Would suspension forks fit? they all look very straight where mine are more traditional with the forward draft?

I think the real fix thats going to work is for me to slow down on such roads and rely less on the motor and more on legs, keeping the motor for uphills and perhaps clean-ish cycle tracks that i can wander the width of more freely to avoid things. in hindsight turning off the cycle track in pas modes 4 or 5 was quite reckless. while i can ride these streets at those speeds i need to be doing so actively my weight on the pedals ready to balance and weave
Not plopped on the seat pedaling air to keep the motor engaged..

My front carry box when full is a PITA as its mass adds momentum to every turn of the steering which speed exacerbates.

When out on the bike today i had the power assist set to 2 when cycling on the flat to just help pulling off loaded with the shop, and only when returning up hill did i step up the assistance..

and thanks for the pointer to Bankrupt Bike Parts could come in very handy..

 

[Scorpio]

Good point about your forks being curved, somebody who knows more will be along soon to comment but my guess it you're right - standard fork would be too straight. If you buy forks be aware there are 2 common types of fitting, "threaded" (look for a large nut below the handlebar stem) or "threadless" (more modern, clamped in place by the handlebar stem).
If I was doing the work again I would buy a fork with fittings for a disk brake on the future (I couldn't fit a brake disk on the original front wheel but I changed the wheel after buying the forks. Oops!)

When carrying shopping I like rear panniers as the weight is low at the back and doesn't affect steering. The only downside is more of the bikes weight is on the back tyre. At one point I had rear panniers + a back box like yours for extras. I also have a basket at the front but I only put light items in that.

Photos of my project https://www.pedelecs.co.uk/forum/threads/kemp-starley-dutch-town-bike-out-of-hibernation.37181/post-582876

 

[guerney]

@guerney Yikes.. I hope the filling reference was a joke to illustrate the jolt you must have endured.

It was, and that set of potholes appeared at 47kph downhill, and I had no time to put my weight on the pedals. There seem to be many more nasty potholes about, than this time last year. The same happened a few times during the journey - that particular area has many industrial units, and that road is frequented by a lot of HGVs; matters exacerbated by the ever increasing numbers of SUVs, which people buy because of all the potholes.

 

[Bikes4two]

Swapping standard forks for suspension ones generally won't work on that bike due to the existing fork 'rake' which sets the front wheel forward of the frame by the amount correct for those frame angles.

And suspension forks can be pricey, at least, the decent ones are, and of course rather heavy in comparison adding to your already heavy overall weight. Suspension forks would also spoil the looks of what is a nice old traditional looking machine.

Might a trailer be a possible solution?

 

[Az.]

I am not sure what is it about big black plastic boxes that attract so many people. It is just a bad idea. Making savings on safety is just a false economy. Changing pressure in tyres will make a little difference. Try proper panniers and you will see the difference.

 

[thelarkbox]

@guerney 47 kph! without warning.. My fillings are coming out in sympathy..

Yeah cycle mechanics has sure moved on since i spent time hammering out wedged in cotter pins and everything was stamped steel or drillium. It can get confusing.. I now know the term 'rake' too , thanks @Bikes4two

Im not convinced disk brakes at the front would benefit this bike? the V brakes work well, I did google the subject one evening including clamps for the front forks that are not disk brake ready. but as said the V brakes work well a sharp pull on the front brake lifts the back wheel as i walk it out onto the rd every morning.

Ive been ridding this bone shaker around and down to the shops since 2020 at speeds i guess 8-12 mph, And yes I NEED a sit down on arriving back home when relying 100% on pedal power, (85% of my trips are uphill on the way home.. which makes setting out fun, but... One direction uphill from here leads to an area of 'good take outs' which is pretty convenient for getting back quick too

But that extra lil oomph accelerating me upto 15mph ?? And my unready mass sat still on the saddle, not the best combo

However ridding as i have the last few days, keeping the power assist for hills and clear runs and not on pas 4 or 5 100% of the time.. much better and i arrive home fresh and alert feeling able to unload the bike and get stuff into the fridge straight away ..

I will accept that watching utubes is not the best prep for anything but it was my intro to ebikes, and ive lost count of the times a review has ended with words similar to " I really like this bike/kit, just set to mode 5/9 and go..." And i believed em

But I now think i might want e-bike #2 too something with suspension and a bit more zip.. Not a road ebike at all

 

[saneagle]

@guerney 47 kph! without warning.. My fillings are coming out in sympathy..

Yeah cycle mechanics has sure moved on since i spent time hammering out wedged in cotter pins and everything was stamped steel or drillium. It can get confusing.. I now know the term 'rake' too , thanks @Bikes4two

Im not convinced disk brakes at the front would benefit this bike? the V brakes work well, I did google the subject one evening including clamps for the front forks that are not disk brake ready. but as said the V brakes work well a sharp pull on the front brake lifts the back wheel as i walk it out onto the rd every morning.

Ive been ridding this bone shaker around and down to the shops since 2020 at speeds i guess 8-12 mph, And yes I NEED a sit down on arriving back home when relying 100% on pedal power, (85% of my trips are uphill on the way home.. which makes setting out fun, but... One direction uphill from here leads to an area of 'good take outs' which is pretty convenient for getting back quick too

But that extra lil oomph accelerating me upto 15mph ?? And my unready mass sat still on the saddle, not the best combo

However ridding as i have the last few days, keeping the power assist for hills and clear runs and not on pas 4 or 5 100% of the time.. much better and i arrive home fresh and alert feeling able to unload the bike and get stuff into the fridge straight away ..

I will accept that watching utubes is not the best prep for anything but it was my intro to ebikes, and ive lost count of the times a review has ended with words similar to " I really like this bike/kit, just set to mode 5/9 and go..." And i believed em

But I now think i might want e-bike #2 too something with suspension and a bit more zip.. Not a road ebike at all

The energy you have when moving on a bicycle is 1/2 x mass x velocity x velocity. That means if you double your average speed, you have four times your previous average energy, and your brakes have to do four times as much work to dissipate it, so brakes that work fine on a normal bike can be quite inadequate when you add a motor and battery. The more work the brakes do, the faster they wear out, the faster they wear the rims and the quicker they go out of adjustment.

Let's say you bike weighed 15 kg, you were 85 kg and travelling at 4 m/s (9 mph). Your energy would be 800 Joules. Now add 6kg electric kit, 5kg of locks and 3kg of luggage and you now travel at 6 m/s (13.5 mph). Your new energy would be 2052 Joules. That's 256% of the work that the brakes had to do before and 256% wear.

 

[sjpt]

Many (?most) riders here don't anywhere near double their average speed when they go electric. My average speed on an ebike till last week was below what it was on a regular bike 10 years ago. My highest speed (downhill unassisted) is also a little lower because I'm more careful than I was.

(My average speed right now is well under 1mph, not on a bike as I've irritatingly and painfully ruptured my knee tendon, so no bike for several months.)