Why is my front tire cupping ?

[Sin_Tiger]

EDIT NOTE : Sin didn't start this thread he just happened to be the first post in the thread that I split it from ................mustang 4/26/2010



I am experiencing the same with my front Anakee on my Varadero which had a complete fork overhaul so it's not necessarily bike realted and shouldn't be down to any fault in the forks. I've seen this observation elsewhere. With the tyre in this condition I feel the front end a bit "light" at speed in as far the slightest change in weight will give a much larger change in direction compared to when they were new. Cornering stability doesn't seem to be affected once the pressure is off the affected section.

To be fair, the have covered over 20,000 kms now in tropical conditions, changing to A 2's shortly as I am otherwise very happy with them.

[Bixxer Bob]

This "ramped" effect is also known as cupping.  It's a common occurence on any heavy bike (my Blackbird does it to any brand of tyre) and is a consequence of weight / braking load and tyre compound.  It's hard to picture, but stay with me....

All tyres have tread (if they're road legal).
As you brake, the leading edge of each the tread block or pattern bites the road surface and is compressed.
The forward force of the bike's weight pushes the tread block leading edge back slightly concentrating the force on that area thus wearing the leading edge more than the rest of the block.

I'll try to do some drawings to illustrate later on when I have some time.

[Bixxer Bob]

Here you go, hope this helps:



In my experience cupping starts to affect handling once it reaches about 1/3 the width of the tread block.  It manifests as washing out in corners, that is to say it starts to run wide and can't hold a line when previously it would (I said that to seperate washing out due to suspension setups etc).   This, I think, is due to the contact patch being only 2/3 of what it was when new.

Just a thought, maybe this should be a seperate post somewhere?

[ArcticTiger]

I have experienced this too, and has been thinking it is related to:
-Incorrect air pressure (to low) compared to load on the wheel,  
-Front and rear wheel not perfectly on the same line.

How often do we check and adjust the air tire pressure when the load changes? Eg.: I ride mostly solo, and has the air pressure set for solo riding. But when we ride 2 up, I dont increase the air pressure, because its "only a short trip" :D

[Mustang]

On the steamers ..certain tires tend to cup more than others .
I have found in my own experience and riding styles that I get the best mileage and least amount of cupping by running 40 to 42 psi air pressure in the front and the rears get 38to 40 psi

michelin tires were always the worst for cupping
dunlops second worse
tourances seem to go south around 5 k

these damn cheap korean shinkos have been marvelous for cupping and tread life the front tire has almost 10k on it and still looks relatively new
I should note that the shinkos have been run with dynabeads in them for balancing also .............I am a believer in the dynabeads after seeing how these shinkos are wearing

http://www.innovativebalancing.com/index.html

from their website............

The result is a smooth, vibration-free ride, derived from our balancing media that is always repositioning itself as the tire wears. If you own a pickup truck, commercial truck, motorhome, RV, tractor trailer, motorcycle, or similar vehicle, and want to get rid of those wheel vibration and tire cupping problems, then you need to move up to Dyna Beads®!

[Rocinante]

With Continental TKC-80 on the Steamer the cupping get so bad towards the end of the tyre life, although the overall wear isn't that bad, that the front oscillates up and down like mad in speeds below 60-70 km/h. I thought something was seriously wrong with my front set-up. I ride with low air pressure though, which probably explains the excessive wear.

One solution is to turn the direction of the tyre for the second part of its wear life. The other is get a new.

[iansoady]

I have found in my own experience and riding styles that I get the best mileage and least amount of cupping by running 40 to 42 psi air pressure in the front and the rears get 38to 40 psi

That sounds very high for the fronts - manufacturer's recommended pressure is around 32psi on the Girly.

[Mustang]

yep but it's what works for me to control the cupping .....but now that I have found Dynabeds I don't check the air pressure much  :oops:

[Bixxer Bob]

Standard (42 psi) front and rear for the 'Bird, standard for the Girly.  Lower pressure will allow more deformation of the tyre and so increase cupping.

[KuzzinKenny]

Wat Bixxer Bob said    + check yer front wheel spins free or this will cause cupping of the front tyre as its like drivin with yer brake on !!

KK

ps cast wheel Tigger tyre pressure is 42psi rear 36psi front but everyone has there own prefered pressures, i run 40/34 !! cos i can  

[Sin_Tiger]

Thanks Mustang ... wasn't sure about whether it warranted copying into the tyre sticky or not.

Good explanation BB, confirmed some suspicions I had   I am happier as soon as I get it leaned over a bit off the square wear region, then she corners fine.

Another thing I have noticed with the "cupping" on these Anakee's is that a few of the tread blocks also have a slight "bobble" in the middle of the wear area, can't expalin that one yet. I am going to try to get a footprint onto some card before I change them out, as it's a bit hard to see in photos.

The new A2's will be going on with dynabeads which I just had delivered, thanks for the tips Mustang  :icon_salut

Sadly the local distributor doesn't stock the range and sizes that I need and they look a bit odd as hand luggage  :(

[Bixxer Bob]

The Tiger's Pirellis don't "bobble" but the Blackbird's Bridgestones do. Maybe I'm just kinder to the Tiger. I think it's just the rubber trearing up a bit when it's working hard.  The rear Bridgestone Battleaxe I used to have on the Trident would tear up pretty bad if I did a few fast motorway miles to get to the twisties and then pushed hard two-up.  I think the fast miles heated the tyre and then the twisties plus the weight tore it up.

On the 'Bird front tyre the wear would start with the leading edge of the tread block rolling back over the block and wearing off when it was new.  Then the the cupping would start.  Then once the front third of the block was worn and so not doing much anymore, the bobbling would start where the contact area began.