[PJ352]

I would take some time to look at other facets of each bikes geo before proceeding. For example, you can't make a direct comparison of two TT lengths without also considering STA's, because that affects reach.

Saddle to bar drop is less of an issue here, because the Le Roi has a slightly taller HT and saddle height is a constant, so it's likely you'll either use the same spacer/ stem setup or possibly less spacers.

Also, check out standover, because if the Izoard in a large accomodated you in that respect, an XL in the Le Roi may not.

 

[PJ352]

Saddle height may be a costant, but wouldn't bb drop as well as HT length effect how that "constant" sits within the fit and interacts with bar drop?

BB drop and HTL together dictate frame stack, so yes, you're correct that even though saddle height is a constant those variables will change the OP's setup... somewhat. But given that he's using a fair number of spacers, is gaining 1cm in HTL (and changing stem angle is an additional option) I don't see saddle to bar drop being an obstacle. Reach, maybe.

 

[PJ352]

The Le Roi is going to have about 8mm's longer reach. Depending on how the Izoard fit, you may or may not need to go with a 90mm stem.

 

[PJ352]

How did you come out to that number? I'm not doubting you, just wondering for my reference.

Could I also just play with the fore aft position of the seat to make up for the 8 mm difference? I had a set back seatpost on the Izoard. Would moving to a zero set back post be a better idea?

Appreciate all the insight by the way!

Fore/ aft saddle position shouldn't be changed to accomodate reach. While a given KOPS/ setback isn't something to be 'married' to, there is evidence that many riders have a range that works best for them, so keep track of that if/ when switching over to the new bike.

For every degree of STA change, reach changes by about 1cm. So if your Izoard has a 557mm TT and a 73.5* STA, going to a 73* STA changes that TT number to 562. The Le Roi's is 570, thus the 8mm difference.

 

[PJ352]

I'm confused.

If the Izoard is at 73.5 and a 557mm virtual top tube and the Le Roi is at a 73 and a 570 virtual top tube, how does that equal out to 8 mm difference according to how you calculated the change? Wouldnt the .5cm (half of the 1cm for every degree of change in STA) need to be added to the 570 since the 73 is more slack then the 73.5?

I probably am just understanding this completely wrong.

To compare two bikes in reach, you equalize the STA's, then using the 1cm per degree of change guideline, calculate the difference in TT length.

We could have gone the other way; equalizing the Le Roi STA with the Izoards by adding .5 degrees. Now, with a steeper STA of 73.5 the TT measurement changes by 5mm's to 565mm's, still 8mm's difference from the 557mm's on the Izoard.