Horse racing house rules looking for advice

Hi everyone. 

I want to make hours racing a way for my players to gamble that can be fun. I have a mechanics idea for this but wanted to run it by the comunity to see what others think. Let me know what everyone thinks. Here is my notes so far. 

I will be honest the constitution part is where I think it might break the race. So any advice there would be good. 

Jockey and horse are one stat block. To build we only need Strength, Dex and Constitution. 

Each stat is 8 +1d4

Each rider gets 1 proficiency point. Rookies get 1 proficiency point, regular riders 2, and pros get 3.

Each race starts with a 1d10 strength to see how far they go each number is 10 meters. So if they rolled a 5 they would only go 50 meters. Next roll a 1d20 Dex, depending on your roll2 or less rider fall off and loses the race, 3-8 is a -2 from the distance (min travel is 3) 9 to 15 no penalty and 16 or up you get a +2 to distance. 

Constitution is stamina, the race is either 1000m or or 2400 meters. You can dash and double your strength distance but you roll a d6 and reduce your Constitution number down that number if you hit 0 your horse goes half speed the rest of the race. The roll would be 1d6-con mod-proficiency modifier with a min of 1. This way if you have a high constitution you can help reduce to loss of stamina and you can dash more

Track the top 3 racers who cross the line. If a jockey wins 10 races he goes up from Rookie to regular to pro. 

Racer Tier Stats Range Odds Payout (on 10g bet)

The Longshot (Rookie) Total < 30 10:1 100g

The Contender (Regular) Total 31–33 5:1 50g

The Favorite (Pro) Total 34+ 3:2 15g 

​To Win: Pick 1st place. (Standard Payout).

​The Quinella (The "Top Two"): Pick the two horses that finish 1st and 2nd, in any order. (Payout: 8:1).  

​The Trifecta: Pick 1st, 2nd, and 3rd in exact  order. (Payout: 50:1). 

Just as a general rule, games within the game are not very fun. If your players want to gamble there are thousands of ways they can gamble outside of D&D. So typically when your players show up at the table they want to play D&D they don't want to gamble (because if they wanted to gamble they'd go do that instead of playing D&D). 

So I'd strongly urge you to forget about complex mechanics and instead focus on some kind of narrative involving the horse racing - maybe one competitor is cheating and poisoning their rival's horses, or maybe one of the riders is secretly casting spells on their horse to give it an unfair advantage, or maybe one of the horses isn't a horse at all but a shapechanger or druid in the form of a horse who is either a willing participant in the fraud or is being coerced into it; or maybe there is a criminal syndicate running an illegal "horse" racing ring with captured magical creatures (unicorns, dire wolves,  displacer beast, etc..) that are being forced to race for the entertainment of others 

What about if I add more mechanics? A 1d8 for cheating or a d12 for inspiration. 

Quote from Blackrigante >>

What about if I add more mechanics? A 1d8 for cheating or a d12 for inspiration. 

 If you sit down to play the Witcher or Skyrim, and find out you instead have to play poker, does it matter whether it is 5-card stud, or Texas Hold 'em? Are you going to be happy? 

I know of a certain adventure that features something very like horse racing. The players can participate as jockeys or trying to stop cheaters.

Disagree minigames are a cornerstone of a lot of games, even in your example,  KCD has farkle, FNV has gambling, Yakuza has a lot of stuff, and even The Witcher has Gwent. As long as you give the player the choice to play in the first place and give ways to get an edge through their statsheets, it can be a great way to spice up gameplay in dnd.

Quote from BaronRusso >>

I know of a certain adventure that features something very like horse racing. The players can participate as jockeys or trying to stop cheaters.

The Wild Beyond the Witchlight: Chapter 1: The Witchlight Carnival: Carnival Locations - Snail Racing

 That would definitely work, if you put the effort into it. Also, see the Tomb of Annihilation rules for Dino Racing for more ideas.