Swapping front chainring for larger size?

[Fordulike]

I'm considering swapping the largest of the front chainrings to something larger.
Then getting rid of the 7 speed DNP 11T for a better quality rear freewheel, but only 14T.
I'm trying not to alter the cadence too much from my current setup.

Currently I believe the front is 42/34/24. What problems, if any, could I come across by fitting a 48T or bigger instead of the 42T?

BTW, I don't use the smaller rings, so would be used only on the bigger chainring!

 

[flecc]

Should be no problems. I've successfully used a 52,38,24 combination on one Shimano geared bike, so the front gear change (if made) between 48 and 34 is roughly the same degree as that.

However, if you currently need the largest rear sprocket at times, you may need to change down to the 34 on odd occasions due to the overall gearing increase of the 48 tooth chainwheel.

If you do go larger than the 48, say to a 52, then I think the second chainwheel would also need to increase from 34 to the 38 to 40 tooth region to ensure smooth front mechanism changes.

 

[Deleted member 4366]

You need yo go up to at least 52T or 53T to get similar cadence. If you want to stick with 48T, the Shimano Deore Hollowtech set can be had for about £70 including BB.
Wiggle | Shimano FC-M590 Deore 9-Speed 48/36/26T Triple Chainset | Chainsets

If you go to 53T you normally find double ones like 53/39, which is about right for an electric bike. You have a choice with the front derailleur. Yu can just move it to get it out the way, and never use it, or move it up and reset everything including the end-stops, which will make it work OK on a double chain-ring.

The main problem that you're likely to encounter is the larger chain-wheel touching the chain-stay, which can be solved with a longer BB.

 

[flecc]

The main problem that you're likely to encounter is the larger chain-wheel touching the chain-stay, which can be solved with a longer BB.

Though on many occasions a subtle dent in the chainstay tube is sufficient! Some models have that dent as standard.

 

[Fordulike]

Scouring eBay I came across this chainset:

white suntour xcr octalink fitting mtb - bike crankset - chainset 48-38-28tooth | eBay

My current setup still has the original Suntour SR chainset and pedal fixtures etc.., so assume this would be an easy swap over.

What has confused me a little is where it says:

axle fitting : shimano octalink

What on earth is that all about? .... Super confused now

 

[flecc]

The Shimano octalink BB uses splined cranks instead of the taper square common fixing:

 

[Fordulike]

The Shimano octalink BB uses splined cranks instead of the taper square common fixing:

So as long as the BB gets changed with the chainset, then compatible with most bikes?

 

[Deleted member 4366]

Octalinks creak something rotten sometimes. Hollowtech is much better. By the time you've bought the BB as well, the price is much closer.
Your 42/11 setup will give a speed of 17mph at a comfortable cadence of 60. The 48/14 will give a speed of 15mph at the same cadence. A 53/14 will give 17mph.

 

[Scimitar]

I put a 52t front chainwheel on mine and ended up taking it off again as the chain kept leaving its fond embrace. I couldn't move the front derailleur up the tube high enough as the battery box got in the way, so ran it without one for a while - with the above results. There's nothing more frustrating than to be bowling along under power, making to stoke the crank, then finding there's nothing there.

 

[jackhandy]

I put a 52t front chainwheel on mine and ended up taking it off again as the chain kept leaving its fond embrace. I couldn't move the front derailleur up the tube high enough as the battery box got in the way, so ran it without one for a while - with the above results. There's nothing more frustrating than to be bowling along under power, making to stoke the crank, then finding there's nothing there.

As John found at the bottom of Park St...

Sorry John - felt a wicked compulsion.

 

[Clockwise]

Adjusting the front derailur can be a real pain, going larger you will usually need to move it up the post it is on a little and then it can take ages to get it right. Sometimes it seems fine but the chain will jump when you have done a bit of biking so for the first few rides it can be annoying.

 

[Fordulike]

Considering I never change cogs on the front chainset, can anyone guide me in swapping my setup to one chainring (48T or larger)

I assume that one chainring without the derailleur changing mech, would need to be lipped on both sides to stop the chain from coming off???

I would like to remove the whole front changing mechanism, cabling, shifter etc..

If I need to change the BB, pedal cranks etc.., then so be it.

Anyone know where I can buy such a setup, if at all?

The bike's a Specialized Hardrock MTB 21 speed

******************************************************************

Would something like this work?

52 TEETH CHAIN WHEEL SET 155mm SINGLE CRANK +GUARD TOOTH CRANK LARGE | eBay

Would I need to change the BB still to fit?
The crank length is slightly shorter. Will cadence increase, offsetting the benefit of a larger chainring?

My head hurts

 

[flecc]

You don't need very much at all, just a new chainring of your chosen teeth size to fit onto your present four arm spider. To choose the chainring you need to know the PCD/BCD*, this being the distance between two adjacent chainring mounting bolt centres. This will probably be 110 mm on your bike, but might just be 130 mm.

Then search for a four arm chainring with your PCD/BCD size or order one from a good bike shop.

Since you are losing the front mechanism chain guidance and spanning the whole cassette of sprockets from the one chainring, I'd advise you use spacers if necessary on the chainring-to-spider bolts to align the chainring with a centre or one higher gear centre rear sprocket. This will minimise the risk of your chain jumping off the chainwheel while changing gears.

* PCD = Pitch circle diameter, BCD = bolt circle diameter, same thing different expressions.

 

[flecc]

******************************************************************

Would something like this work?

52 TEETH CHAIN WHEEL SET 155mm SINGLE CRANK +GUARD TOOTH CRANK LARGE | eBay

Would I need to change the BB still to fit?
The crank length is slightly shorter. Will cadence increase, offsetting the benefit of a larger chainring?

My head hurts

The cadence won't increase due to a crank arm length reduction of course, but will reduce at a given road speed when changing to the 52 tooth. Reducing cadence and crank arm length at the same time is not a good idea since they accentuate each other's effect. The shorter arm gives less leverage just as the slower cadence requires more for a given effect.

That one will be ok, but as said, you only need a chainring for your existing cranks and four arm spider.
.

 

[Fordulike]

Thanks flecc, I think I tried to make the task harder than it really is.
I'll give it a go and post back here with my attempt

The leverage problem won't affect me in my case, I just needed to find a solution to replace the rear freewheel for a higher quality one, unfortunately increasing teeth count from 11T to 13 or 14T.

Changing the front chainring at the same time, means I won't be pedalling like my legs are on fire

 

[flecc]

It's not a difficult job, the main thing will be trying to find a four arm 52 tooth with the right PCD, since most larger chainring setups use five arm spiders. Let us know if you hit problems in finding one, someone may know a source and you can even have one made for you if necessary.

 

[Fordulike]

It's not a difficult job, the main thing will be trying to find a four arm 52 tooth with the right PCD, since most larger chainring setups use five arm spiders. Let us know if you hit problems in finding one, someone may know a source and you can even have one made for you if necessary.

Yes, I did notice that the majority are five armed.
I'm sure I'll find one somewhere. No rush, I like to make sure everything is watertight before I commit to changes.

 

[Fordulike]

To make the changeover less hassle and considering the original crankset is Suntour, I think I may go for the components in the links below:

suntour xcr v2 bike -mtb crankset with bottom bracket | eBay

Sunrace 7speed road freewheel.13-25 Chromed.New | eBay

Now if I've done my homework correctly, then swapping from a 42T chainring and 11T freewheel will be almost the same as the above, a 48T chainring and 13T freewheel.
The only thing that concerns me is that the freewheel states for road bike.
Would it be compatible with a MTB bike?

I would be grateful if a forum member could take a little time out to cast an eye over this and tell me if I'm doing the right thing. Thanks in advance

 

[flecc]

The freewheel should be ok since the freewheel threads on road and MTB bikes are usually the same, just BMX using smaller mounting threads. The mention "for road bikes" probably refers to that narrow range of sprocket teeth, a set for MTB typically a wider range like 13 to 30 or more.

So you could buy that lot, but it seems a pity to scrap so much of what you have which is still serviceable. If you do change to it you can unbolt and remove the two smaller chainrings since you wont be using them.

 

[Fordulike]

The freewheel should be ok since the freewheel threads on road and MTB bikes are usually the same, just BMX using smaller mounting threads. The mention "for road bikes" probably refers to that narrow range of sprocket teeth, a set for MTB typically a wider range like 13 to 30 or more.

So you could buy that lot, but it seems a pity to scrap so much of what you have which is still serviceable. If you do change to it you can unbolt and remove the two smaller chainrings since you wont be using them.

It does seem a shame not to use what I've got, but I've searched the last hour for a 4 arm 110mm BCD chainring to suit, but drew blanks.

Felt it was less hassle to replace the lot as one.
Didn't realise that you could unbolt the middle and small chainring. Thought they might form an integral part of the system, so thanks for that info