Technical > Wheels, Tyres and Brakes

differerent front and rear tyre combo?

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pondweed:
Is anyone running with different spec front and rears?
I'm still weighing up between 2.0 and 1.6 Supremes for Sherpa, but wondered whether anyone was running with larger front tyre for potential suspension effect or slackening geometry slightly? Or has experimented in this field?

mickeg:
I always use the same size up front as the rear but sometimes use a different tread. For example, I have done several trips on my Sherpa with a Marathon Dureme up front and Marathon Extreme in the rear, but both were 50mm wide.

I consider sizes to be the same if they are within 2mm of each other, thus I consider 35mm and 37mm to be the same.  On my 700c touring bike I am contemplating mixing an old Marathon XR (35mm) on the rear with a Hutchinson Globetrotter (37mm) front.

I might on future trips run a Marathon Dureme (55mm) in front and Marathon Extreme (57mm) rear on my Nomad.  To date I have run the Extremes on both front and rear for touring, but I have a 55mm Dureme that I might use instead.

martinf:
I've run different size tyres on 2 bikes, just to use up tyres.

32 mm front and 38 mm rear on a Brompton.

44 mm front and 50 mm rear came on my old mountain bike, it now runs on 50 mm front and rear.

Didn't notice any geometry issues with either setup.

Danneaux:

--- Quote ---Is anyone running with different spec front and rears?...Or has experimented in this field?
--- End quote ---
Well...sure. This is one reason why I wrote the article on trail and handling (the other reason is I am a hobbyist framebuilder and I enjoy the design aspect as much as building).

Not all that article was theoretical; I have indeed mixed tire sizes on the same bike and would suggest it to you as an empirical way to gain insight to how tire size affects trail and handling. One shortcut is to mix large differences in tire size, as small differences don't make much ehm, "difference" to handling, as George and Martin have noted. 26in wheel tires are generally available with big "jumps" between tire sizes, so sure...try a 2.0in tire at one end and then the other while keeping your preset 1.25in tire at the other and see what happens.

One major note here: It is desirable to adjust pressures to suit the tire sizes, so narrower tires with less air volume get higher pressures while bigger, fatter tires should get less pressure. This pressure difference can cloud the effects of mixing tire sizes, so I would suggest putting in pressures that result in the same "rim drop" under identical load (keeping in mind the caveat to avoid overpressurizing fat tires, as this can adversely affect rims by resulting in jacking forces high enough to crack or split a rim).

I will note, having tried mixed tire sizes in the past, I returned to two tires of the same size...notsomuch because I didn't like the resulting and slight change in geometry, but because I did not like the difference in tire contact patch shape and size (one tire patch is longer and narrower, the other shorter and wider). I felt that affected handling and cornering more and made a bigger (and unpleasant) difference in bike response than I wanted.

Sheldon Brown discusses mixed tire sizes about 2/3 of the way through the article at this link:
https://www.sheldonbrown.com/tires.html

If you are still having handling issues with your Sherpa, the I would do two things:
1) Try fitting two wider/fatter tires of the same size and see if that solves your problem...the present 1.25in tires you mentioned using in an earlier post are considerably smaller than are generally used on a Sherpa. Looking back at my pre-purchase notes, SJS Cyles staff told me my Mk2 Sherpa was designed around 1.6in tires, my Nomad was designed around 2.0in. I could certainly notice a difference when I replaced the 2.0in Schwalbe Duremes used on my Sherpa and Nomad with the 1.5in road slicks I borrowed from my tandem.

2) I would suggest some of your handling difficulties may relate as much to your (used) bike's size and/or how it is fitted as it does to the tires.

In the scheme of things, buying and trying one or two different tires than you have now or fitting a different stem or seatpost are relatively inexpensive and can go far toward dialing in the feel of the bike and making it closer to what you prefer.

Have you sent your dimensions to SJS Cycles to check you are indeed riding a size within range of your body type and preferred seating position? Though we may each fit a variety of frame sizes, individual variations in body part size can make a big difference to comfort, setup and on-road handling, i.e. whether you have long or short arms/legs/trunk for your height and need to accommodate for same.

Hopefully helpful.

Best,

Dan.

pondweed:
Interesting stuff from all thanks.

I think Dan has brought up the real issue. I was wanting to try the 'trail' variation thing (and it seems that the most interesting thing would be to put a biggie on the front) but the comment on contact patches and affecting handling makes me realise that it really would just be experimentation. I will definitely put the biggie on there from my mtb, if it will fit with the mudguard, as a 1.25 up to a 2.1 might trigger some form of geometry difference I'd like to experience. I read on some Single Track forum some chap mentioning wanting to 'slacken the angle'...

Dan's other point on the sherpa being designed around 1.6s makes me realise I've got to get those over the 2.0s too, as a datum.

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