Hey all you SRM gurus and anyone else that reads this. I have 2 bikes, one 650 TT and a 700 road bike.
Two questions:
First, I am buying an SRM and I use a 54-42 on the 650 and a 53-39 on the 700. What should I do with th e SRM?
Also, what about crank lengths? Go with the shorter or longer that I use (170 vs 172.5)?
Thanks,
Rob
first, cant speak to the crank length exactly. but i would say go with what you feel suites you best. i am six feet, 31inch inseam, pretty normal proportions, i run a 175. have tried 177s on my tt bike but i can feel the difference and have tweaky knees at times so all are 175.
as far as gearing, i would reocmmend a 54 shimano outer ring and 39 inner. gives you best of both worlds. s himano does NOT recommend this gearing. you’re supposed to choose 2 rings (outer/inner) from their A group or 2 from the B group. that is, they say a 54 wont mate well with a 39. we have about 4 team riders who all run it this way since it is difficul tto afford multiple srms for road, vs. tt bikes.
i personally , on my race rig, run a 54/39. shimano rings. i’m a fairly comeptitive cat3 that does a ton of aggressive road racing with tons of shifting requirements, and i also do quite well on the tt bike. i have never considered that gearing to have shifting issues.
i will say that i fyou cross index a lot, small small. that is you run it in the smallring (39) and then let the gears drop down to, lets say a 12, hence 39x12 you’ll get al ot of rubbinh, mor a reminder that hey, you’re in the wrong gear. but outside that, shifts are just fine, no dropped chains, no rubbings, and ou get the fat 54 for hammering, and the 39 for climbing.
also, side note, you can also take the first 4 cogs of a dura/ultra 10speed 11-23 cassette and mate them to the back 6 of a 12-25 and you end up with a very desireable 11-25. expensive if you dont get the cogs at cost, or on ebay. but you get an 11-25, power on the flats/descents, and a lite 25 climbing gear. or, i have enjoyed the SRAM 11-26 for the same reason, althought its a bit heavier, but not by much.
good luck.
Thanks for the info. I am not as tall as you are and I hesitate to have such a large diff in the front chain rings for the reason of chain drop potential and cross chaining. However, I see the obvious benefits. I am going to work out the gear ratios as well. I like the suggestion for the rear casette. I appreciate your knowledge. Thanks again.
Send a PM to Kurt Perham (trukweaz) if he doesn’t respond to your post.
I have a SI SRM that I swap between bikes in less than 5 mins. More around 2.5 if I’m in a hurry.
But, your situation sounds like a pain in the ass b/c you’ll have to reconfig on your wheel size to get the proper readings.
As for chain rings, IMO go standard. I don’t see what the 42 is really offering other than a tiny bit of weight.
Length…I dunno, depends on which ones are the proper fit currently.
Good luck.
When I had a 650c tri bike I used 56/44 chainrings on that bike and 53/39 on my road bike. It only takes a few minutes to swap the chainrings and is a small amount of time if you’re moving the SRM over to another bike anyway.
Robert, you will not want to make ring changes on the SRM, the rinsg hold the cover for the electronics on so you have to be very careful and not rushed.
I would choose the ring combo for the bike you ride the most, then adjust the cassette for the other bike.
I would think a 39/53 for both, then maybe a 11-23 or 11-21 on the 650 bike.
Kurt
Thanks to all. Kurt, I will be contacting you about the SRM ASAP.
I think that the issue that I have will be remedied by smart use of rear cogs and repetition with the SRM.
Train smart!
Rob