Will it make the handling for my road bike difficult?
In my opinion yes it’s too short.
do a search as i’m pretty sure dan wrote an article a while back about front end handling of road vs. tri bikes. i’m paraphrasing but i “think” he said that due to the distribution of weight on the front end, shorter stems on bikes with steep geometry do not adversely affect the handling as much as shorter stems on road bikes where more weight is over the rear wheel.
free bump though as i can’t recall for sure.
also on a tri bike, where your aerobars place the elbow pads will affect the “effective stem length”
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Not sure what is right or wrong, I did a lot of research/reading on this topic and found a lot of information stating against it. But, I got a very good deal on my bike and that is what it took to make it fit, so I gave it a shot. So speaking from my personal experience it works out just fine. I don’t have any trouble at all with the handling of the bike, it has worked out great for me. I also know someone else who I ride with sometimes who also has a 70mm and has not had any issues. If you were buying a new bike, I would say to get a size to avoid this, but if it is what you need for something you already have or a deal you can’t pass up, I say no big deal based on my experience. Both of the bikes mentioned above are TT bikes, one QR and on Cervelo.