Braking and handling questions

[appalachian ape]

Hey all, I posted this question on bikeforums,whi h was a waste of my time and energy.. so much douchebaggery there! So here goes.
I hot a 2022 eahora xc100. 160mm rear Cable disc brakes and upgraded to 203mm front. Front feels good now, but rear.. hard to describe but, hard braking rear wheel feels loose or squirmy almost like a flat tire feeling.
What are some things I could look at to see what the culprit might be? I am leaning toward maybe a slightly warped rotor, spokes are tight, tire properly inflated, wheel is tightly bolted in dropouts. So I'm lost

Thanks a lot

 

[matthewslack]

Hey all, I posted this question on bikeforums,whi h was a waste of my time and energy.. so much douchebaggery there! So here goes.
I hot a 2022 eahora xc100. 160mm rear Cable disc brakes and upgraded to 203mm front. Front feels good now, but rear.. hard to describe but, hard braking rear wheel feels loose or squirmy almost like a flat tire feeling.
What are some things I could look at to see what the culprit might be? I am leaning toward maybe a slightly warped rotor, spokes are tight, tire properly inflated, wheel is tightly bolted in dropouts. So I'm lost

Thanks a lot

More description might be needed if responses seem off the mark.

On the limit i.e. about to lock the wheel, normal rear behaviour is for rear to want to overtake the front. Weight transfer forwards reduces adhesion, and limits how much braking power can be provided by the rearwheel. For maximum retardation, really good control of a powerful front brake is key.

Does any of that help?

What kind of surfaces does the issue arise on?

 

[appalachian ape]

Hey Matthew, thanks for the response! Mowed all of my writing is on paved roads lots of Hills on my commute. It's not when I lock up the brakes it's not skidding, at least far as I can tell cuz I'm not squeezing that hard it just when I first hit those back brakes it feels like a shimmy or like if you are running with a low tire pressure. It feels like it's wobbling right to the left very slightly but enough to be unnerving does that make sense?

 

[matthewslack]

Hey Matthew, thanks for the response! Mowed all of my writing is on paved roads lots of Hills on my commute. It's not when I lock up the brakes it's not skidding, at least far as I can tell cuz I'm not squeezing that hard it just when I first hit those back brakes it feels like a shimmy or like if you are running with a low tire pressure. It feels like it's wobbling right to the left very slightly but enough to be unnerving does that make sense?

Is it like one movement, or oscillating left and right multiple times?

 

[appalachian ape]

Left right wobble

 

[matthewslack]

Left right wobble

You could try different, probably higher, tyre pressures or different tyre, but if that makes no difference then it sounds like flexibility in either the frame or the wheel.

 

[Nealh]

I have never experienced this effect with rear braking so agree, it is proabably a wheel issue or a frame issue.
With the frame it could be crack or maybe the movement in the dropouts ?
A part from the tyre and psi, are the spokes correctly tensioned and are the bearing all good.

 

[flecc]

Are the wheels in line? Turn the bike upside down and see if you can sight along both wheels with them exactly in line, with the front and rear of both wheels all in exact single alignment. With a dished or offset rear wheel it's not unusual for the rear wheel to be following a slightly different track from that of the front wheel.

When riding normally that doesn't matter, some are even designed that way, for example Burrows 8-freight has it's rear wheel following a very different line from the front.

But under rear braking the drag of the rear wheel tyre on the road can try to move the wheel sideways to exactly follow the front, but then try to correct back to out of line as it achieves that, giving such a squirming feeling side to side.

If that is the cause it's perfectly safe and self correcting, just feels a bit odd. Just lead with the front brake with minimal support from the rear one.
.

 

[matthewslack]

The only other thing I can think of is the effect of the position and weight of the battery.

My bike in normal mode has 3kg on the downtube, and nothing on the rear rack. In Mk 1 solar mode, there is nothing on the downtube, but 6kg rigidly mounted to the rear rack. Although I had no issues of instability, the feel of the different weight distribution, both height and longitudinal position, was very noticeable.

If yours is a rack mounted battery, check if the rack is rigidly mounted to the bike frame.

I would also try test rides at both the maximum and minimum tyre pressures advised on the sidewall of the tyre to see if there is any difference.

 

[AndyBike]

Paved roads the tyre pressure should be about the maximum the tyre is rated for. Firmer tyres equals less surface area equals less drag.

 

[Nealh]

I don't agree with the riding to max psi on paved roads, my bike rides fine with tyres at 40 - 50 psi instead of the max 80 psi.

 

[appalachian ape]

Hey all, wanted to follow up on my braking issues, i have a few hundred miles on the bike now, and I am not feeling that sensation anymore, I am guessing it was more about adapting to the feel of the bike.
Ona side note, I had swapped my front brake from 180 to 203mm and i realized that EAhora (the ebike company) supplied the bike with shifter cable housing instead of brake housing.. which explains why my stopping power was nearly non-existent!!!

 

[saneagle]

Squirming under breaking = steering head bearings need adjusting.

 

[soundwave]

on the road with my front tyre if i push it to hard at 30psi+ it starts to slide sideways with high speed corners going 30mph but im just nutz lol but im still n ot dead either