I’m having a wheelset built up by Light Bicycle for road/tri. The rims are 55mm rear/45 front. I plan on putting Conti 5000 TR with Vittoria liners. My question is, which would be the best combination of tire width for both speed and handling (especially technical mountain descents): 25 mm front and rear; 28mm front/rear; 28 rear/ 25 front? Some other size combo?
What’s the width of the rims?
It’s likely a 28/28 will be the fastest/best unless the rims are optimised for a 25.
Other than that… Don’t overthink it.
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25f 28r will be fastest in pretty much all but shit road conditions
But 28/28 might be necessary if hookless
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hooked rim, 21mm internal/28 external
Depends on the amount of crappy pavement? I’ve got 21mm internal rims with 35mm external on the front - yes thats wide - and often put 25 or 26c tires for speed. The rear is not as wide, think its 30mm external, and I use 32c tires to reduce punctures or 28c tires if I want to see if punctures go up (they do, every tubeless tire, ever).
The only time I notice handling issues is when riding over crappy pavement, or loose rocks. Technical mountain descents on crappy pavement or gravel is a winning combination for going wide.
I use 25 (26.5 actual) front, 32 rear GP5000 S TR on Light Bicycle AR465 (28-30 width) that are 46.5 depth front and back. I originally had a 30mm tire in the rear but the tire got slashed by a razor and I could only get a 32 on short notice. No regrets, but I eventually got another 30 as backup.
so do you feel like 25/30 is a good combo for speed and handling?
I wasn’t running tests so I can’t say with scientific rigor, but yes. I ran 25 instead of 28 in the front for aero effects, especially against crosswinds.
I’ve done 25/28 F/R by necessity in the recent past when there was a tire shortage. Honestly couldn’t tell the difference either way. Pretty much forgot that had the reverse semi-mullet setup until I eventually flatted.
I run 26/28 on my training wheels. Honestly it’s probably not worth faffing about. I might just run 30s soon either way. Don’t really care about speed on those wheels, lol!
its been gusty AF for the last 3 months, and I honestly can’t tell the difference between running front tire at 26 or 28 or even 34 last season. Its all crosswinds, all the time except in the winter.
Small rocks in the road, those mostly disappear with 32s on the back. Anything smaller and the bike (Tarmac SL7) will skip a little (I weigh over 90kg).
@kurt.braeckel forget to tell you a month ago on Wed worlds a guy with Pirelli Cinturato (26 I think) hit a large pothole at 28mph and he had to put a Dynaplug in to seal a hole in the rear tire! And he is a little guy, maybe 65kg. He was going to make the call of shame and two of us pulled out dynaplugs
Don’t hit the pothole! 
I’m on my second set of Cinturatos in the last 10 months and they’ve been bombproof for me. Perfect training tire if you’re willing to sacrifice a bit of speed to keep rolling day after day.
My guess it’s more mental (delusion) than any real world (non-racing) impact. But I fall to the delusion anyway.
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